The invention relates to a magnet pole of the type, and a method for the production thereof.
Magnet poles of the stated type are used in magnetic levitation vehicles and, in this case, in magnet systems of support magnets, for example. They mainly comprise an iron core and a coil in the form of a strip of aluminum or the like, which has been wound onto the circumferential surface of the iron core (e.g. DE 197 03 497 A1, DE 10 2004 011 941 A1). For protection against environmental influences such as moisture, the magnet poles are also encapsulated in a protective layer made of a plastic which comprises an epoxy resin, for example, is relatively hard, wear-resistant and inflexible, and provides protection against corrosion and mechanical stress.
The undersides of the iron cores typically remain free of protective layers. The main reason for this is that the undersides of a plurality of magnet poles of a magnet system are usually interconnected by so-called magnet rear sides for magnetism-related reasons, or other reasons, which are likewise made of iron and are pressed against the undersides of the iron cores using springs or the like (e.g. DE 34 10 119 C2, DE 10 2004 012 743 A1). Due to this measure, the coils are usually wound onto the iron core such that a narrow gap remains between them and the undersides of the iron cores or the upper sides of the magnet rear sides, and the coils therefore always permit the desired close fit of the magnet rear sides against the undersides of the cores despite typical tolerances. The protective layers therefore verge laterally onto the circumferential surfaces of the iron cores in these regions.
During operation of such magnet poles, relatively high currents are conducted through the coils, thereby causing the coils to heat up to a great extent. Due to the different thermal expansion coefficients of iron and the coil material, the result is that the coils expand further in the radial direction than do the iron cores. As a result, there is a risk that the elongation at tear of the protective layers which are typically used and which are fixedly connected to the coils will be greatly exceeded at critical points. In this context, the points at which the protective layers verge laterally on the circumferential surfaces of the iron cores have proven critical above all.
The protective layers are subject to particularly strong mechanical stresses in the critical regions when the electromagnets equipped with the magnet poles are switched on and off in cycles, as is the case, for example, with support magnets of a magnetic levitation vehicle due to the constant switch between vehicle operation and pauses in vehicle operation. As a result, cracks forms in the protective layers and/or gaps between the circumferential surfaces of the iron cores and the end faces of the protective layers adjacent thereto, thereby permitting moisture to enter the interior of the magnet poles and, over time, destroy the insulation between the coils and the iron cores. Leakage currents induced as a result render the magnet poles unusable if they reach a certain size.